Mount Weather was designed to be a secure location to evacuate the President and other high ranking members of government to in the event of catastrophic attack or national disaster. The other one we found was at Raven Rock, a backup facility for the Pentagon. There are probably others such as Warrenton and the Cheyenne Mountain Complex, but most were designed to support continued life for far less than a century and several had been decommissioned. They also might not exist in this world. Probably most of the population is made up of other Grounders.